Similar to the IE6 situation, when using HTML5/CSS3 in our websites, it is a good idea to offer non-problematic outputs to web users with older/non-standard browsers.

Modernizr is a JavaScript library that uses feature detection techniques to determine whether or not the current browser is capable of CSS3 and HTML5 features like rgba(), border-radius, CSS Transitions & more.

It enables you to write pseudo-IF/ELSE statements in your CSS &, if wanted, it is possible to wirite conditional statements in JavaScript with the help of a "Modernizr JavaScript object" created.

Also, Modernizr adds support for styling HTML 5 elements. This allows you to use more semantic, forward-looking elements such as <section>, <header> and <dialog> without having to worry about them not working in Internet Explorer.